Field of the Invention
The present invention relates to a negative electrode active material for a non-aqueous electrolyte rechargeable battery, a method of fabricating the same, and a non-aqueous electrolyte rechargeable battery including the same. More specifically, the present invention relates to a negative electrode active material for a non-aqueous electrolyte rechargeable battery, which includes SiOx having an O/Si molar ratio of 0.5 to 1.6, a method of fabricating the same, and a non-aqueous electrolyte rechargeable battery including the same.
Related Art
Recently, according to the remarkable development of portable electronic apparatuses, communications apparatuses, and the like, a development of a rechargeable battery having a high-energy density has been strongly demanded. At present, as a rechargeable battery having a high-energy density, there are a nickel-cadmium battery, a nickel-hydrogen battery, a lithium ion rechargeable battery, a polymer battery, and the like. Among these, since the lithium-ion rechargeable battery has a remarkably longer lifespan and higher capacity than the nickel-cadmium battery and the nickel-hydrogen battery, it shows a strong growth in demand in a power supply market.
As a conventional negative electrode active material of a lithium-ion rechargeable battery, a carbon-based material has been used. As a new negative active material which allows the lithium ion rechargeable battery to have a higher capacity than a conventional lithium ion rechargeable battery, a lithium-boron composite oxide, a lithium-transition metal (V, Fe, Cr, Mo, Ni, etc.) composite oxide, a compound including Si, Ge, or Sn, N, and O, Si particles whose surfaces are covered with carbon layers using a CVD method, etc. have been proposed.
However, although these negative active materials increase charge/discharge capacity to increase an energy density, expansion or contraction may increase during adsorption or release of lithium ions. Thus, the lithium ion rechargeable battery using these negative active materials has insufficient retention of discharge capacity due to repeated charge and discharge (hereinafter, referred to as “cycle characteristics”).
Recently, it has been tried to use a silicon oxide powder represented by SiOx (0<x≦2), such as SiO, as the negative active material. Although silicon oxide may be represented as SiOx, it has a structure in which amorphous silicon and crystalline silicon having sizes of several tens of nanometers are dispersed in silicon dioxide when observed using a transmission electron microscope (TEM) analysis. Thus, SiOx has battery capacity smaller than that of silicon, but 5 to 6 times greater than that of carbon, experiences a relatively low volume expansion, and is easy to be used as a negative active material. However, since SiOx has a large irreversible capacity and very low initial efficiency of about 70%, there are problems in that it requires excessive battery capacity for a positive electrode and thus a large amount of materials for the positive electrode when a battery is actually fabricated using SiOx. Accordingly, SiOx is economically infeasible and it is difficult to increase battery capacity corresponding to 5 to 6 times capacity increase per active material.
In Patent Document 1, a carbon film is formed on a surface of a particle (a conductive silicon composite) having a structure in which crystalline silicon is dispersed in silicon dioxide. However, there is a limit to increase the initial efficiency.
In Patent Document 2, a film including lithium fluoride is formed on a surface of SiOx in order to suppress cracks or defects of a negative electrode active material for a non-aqueous electrolyte rechargeable battery, which is confirmed by XPS analysis. However, aside from improved cycle characteristics of the battery, whether or not the initial efficiency is improved is not disclosed.
In Patent Document 3, a binding energy value of silicon and oxide is represented by a ratio of a core formed of SiOx to a shell including a metal oxide layer. However, aside from improved thermal stability and cycle characteristics of the battery, whether or not the initial efficiency is improved is not clearly disclosed.